When signing in with two-factor authentication, setting it up, or changing your email address, the form now submits as soon as the six-digit code is complete. That includes a code pasted with a space in the middle, such as 123 456, and one filled in by a password manager. If the form still needs something else, such as your password, it waits for you to press the button.
Codes submit themselves
Six-digit sign-in and confirmation codes now submit as soon as the sixth digit is in, including when pasted or filled in by a password manager.